The invention concerns a method for marking a feature substance, present in particular in pulverized form, with at least one marker. The invention furthermore concerns a security feature having the marked feature substance for the safeguarding of value documents, a value document having such a security feature, and a method for checking the authenticity and/or the origin of the value document.
The safeguarding of value documents against forgery by means of security features has been known for some time. Feature substances are known that are based e.g. on magnetic, thermal, electrical and/or optical (e.g. absorption and emission) effects, through which the specific detectability is guaranteed.
Of special importance are luminescent feature substances. In such substances the luminescent components used are substances (which will hereinafter also be designated as luminophores) that are able to emit light with a characteristic spectral distribution after excitation (e.g. by light, heat or by an electrical field). They are preferably formed from host lattices doped with transition metals or rare earth metals as luminescent ions (there also being employed hereinafter the term matrix instead of the term host lattice). For the doping, combinations of transition metals and/or rare earth metals have also been discussed, see e.g. WO 99/38701. Transition metals ions or rare earth metal ions have the advantage that, after being suitably excited, they show one or more characteristic luminescences which facilitate a reliable proof and the delimitation over other spectra. The emission of the employed luminophores is also designated as luminescence, whereby this may involve fluorescence and/or phosphorescence.
The security features are incorporated into and/or applied to value documents in different forms of use. In particular, in the case of luminescent feature substances there can also be employed a combination of luminophores whose emissions differ with respect to their spectral and/or temporal properties. The emission bands of the employed luminophores constitute a spectral coding.